This is a randomized, partially double-blind trial for ACTG 302/303 participants who were originally randomized to d4T monotherapy or new combination nucleoside therapy who remain on their original treatment at the time of enrollment into this rollover protocol. Subjects will be stratified on the number of new nucleoside analogs they will receive (1 or 2), relative to the ACTG 302/303 combination they received. Subjects will also be stratified based upon a plasma HIV RNA level > 500 copies/ml. Primary objectives will be to determine the proportion of subjects who acheive a plasma RNA level below the limit of detection; to determine the absolute change in HIV RNA from baseline to week 16; and to assess the safety and tolerablity of Nelfinavir and DMP-266 in nucleoside containing regimens.